Concentric smoking filter having cellulose acetate tow periphery and carbon-particle-loaded web filter core

Abstract: A concentric smoking filter 12 in which the peripheral filter 20 medium is a fibrous tow, such as fibrous cellulose acetate tow, and the core filter 21 medium is a web material, such as paper, loaded with carbon particles 24, is provided. The filter improves the taste, particularly, of "ultra-light" cigarettes.

Description: This invention relates to smoking filters, and particularly to concentric smoking filters. More particularly, this invention relates to concentric smoking filters having tow and web filter media portions arranged concentrically. Most smoking filters, particularly cigarette filters, sold commercially as part of cigarettes consist of a cylindrical rod or "plug" of a "tow" of plasticized cellulose acetate fibers. Some filters are variants of the standard filter, having recessed mouth ends, or being made of two plugs placed end-to-end with a space in between, the space being either empty or filled with another material such as charcoal. It is also known to provide such filters having multiple plugs abutting one another, the different plugs differing in density or other characteristics. Similarly, it is known to provide filtering media other than cellulose acetate. One such medium is an appropriate sheet or web material. The web material, which is gathered into a cylindrical plug, can be paper or any other web material, including cellulose acetate in sheet form. When such web material are used as filters, they are frequently corrugated before being gathered. Paper webs may also be creped to improve tensile strength and elongation properties. Some of these different materials and different constructions have been combined. For example, it is known to provide filters having two or more abutting plugs, at least one of which is cellulose acetate tow, and at least one of which is a web material. Finally, it is known to provide "concentric filters" in which two different forms of cellulose acetate tow --different, e.g., in density -- are formed in to a filter. One cellulose acetate tow forms a cylindrical "core", while the other tow forms an annular peripheral layer. EP-A-0 474 940 discloses a ventilated smoking filter having a resistance to draw of for example between 130 and 160 mm water, a filter plug itself comprising a central core of gathered corrugated web material having a resistance to draw of for example between 350 and 450 mm water and a peripheral layer of cellulose acetate tow. US 3 396 061 discloses a filter of very low pressure drop, for example 36 mm water, comprising a paper central core and a cellulose acetate peripheral layer. One or both parts of the filter may include a selective filtering agent. Smoking filters are characterised by various parameters, including pressure drop, which is referred to as resistance-to-draw ("RTD") and usually measured as the height of a column of water, and efficiency, which is measured as the percentage of the total particulate matter ("TPM") in the unfiltered smokestream that is trapped by the filter. The RTD of a filter affects how smokers perceive the filter in terms of how hard they must draw on it to receive a desired amount of smoke, while the filter efficiency controls the amount of TPM delivered in the smoke. It has been found that while web filters, and particularly paper filters, are more efficient than tow filters, the web material, especially paper, adds an off taste to the smoke which decreases smoker satisfaction. In addition, the appearance of the visible deposited smoke components on the end of a paper filter is much less regular, and more spotty, than on a cellulose acetate tow filter, again affecting the aesthetic impact on the smoker. This difference in appearance is believed to result from the channelling of deposited material in the channels formed by the corrugation and gathering of the web during plug making. As consumer preferences tend toward lower delivery cigarettes, the need for higher efficiency filters, which allow lower delivery without increased filter RTD, increases. However, the higher efficiency of paper filters could not previously be taken advantage of because of the negative consumer impacts of paper filters. It would be desirable to be able to provide a high efficiency filter which produced low delivery while also delivering acceptable taste, RTD and other aesthetic impacts. It has been desired to provide a high efficiency filter which produces low delivery while also delivering acceptable taste, RTD and other aesthetic impacts. In accordance with this invention, there is provided a smoking filter comprising; a first filter plug comprising: a central core of a gathered corrugated web filter material, and a peripheral layer of a fibrous tow filter material surrounding the central core; the central core having a resistance to draw of between 285 mm W.G. and 500 mm W.G. and the filter having a resistance to draw of between 115 mm W.G. and 225 mm W.G., to, in use, initially direct a greater fraction of smoke through the peripheral layer than through the central core whereby smoke initially directed into the peripheral layer flows back into the central core; the filter plug including means for admitting ventilation air into the peripheral layer, characterised by the first filter plug further comprising: carbon particles distributed throughout the central core, having a size distribution such that 94% of the particles are between about 20 mesh and about 70 mesh, a moisture content between 15.5% and 20.5% by dry weight of the carbon particles, and CCl 4 activity between about 50% and about 60%. When the filter is attached to a smoking article and the smoking article is smoked, the filtered smoking article delivers smoke containing a particular level of total particulate matter, and the taste of the smoking article is a taste associated with smoke having a level of total particulate matter higher than that particular level. Preferably, the central core contains between 5 and 35 mg of carbon particles. A dual filter including the first filter plug and a conventional second filter plug is also provided. Brief Description of the Drawings The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: FIG. 1 is a mouth end perspective view of a cigarette having a first embodiment of a filter according to the present invention; FIG. 2 is a radial cross-sectional view of the filter of FIG. 1; FIG. 3 is a mouth end perspective view of a cigarette having a second embodiment of a filter according to the present invention; and FIG. 4 is a mouth end perspective view of a cigarette having a third embodiment of a filter according to the present invention. Detailed Description of the Invention In accordance with the present invention, it has unexpectedly been found that when a concentric filter is made with paper or other web material in the core, and cellulose acetate tow in the periphery, or vice-versa, not only is high filtration efficiency achieved without the introduction of an off taste from the paper, but a cigarette with low TPM delivery can be produced which has the taste of a cigarette with a higher TPM delivery. As shown in FIGS. 1 and 2, cigarette 10 includes a tobacco rod 11 and a first preferred embodiment of a filter 12 according to this invention. Tobacco rod 11 is wrapped in conventional wrapper 13, while filter 12 is wrapped by conventional tipping 14. Filter 12 includes cellulose acetate tow peripheral layer 20 and central paper core 21. Cellulose acetate peripheral layer 20 is a conventional cellulose acetate tow, preferably wrapped by porous plug wrap 22, although self-supporting filter rod technology, such as steam bonding or spray coating of the outer surface of peripheral layer 20, can be used to make a filter that need not be wrapped, if desired. Paper core 21 is a paper web that has been corrugated and gathered into cylindrical form and wrapped with plug wrap paper 23. Plug wrap 23 improves the processibility of core 21 as well as its aesthetic appearance, and also helps to assure substantially perfect concentricity. Flavorants or other additives, such as soluble tobacco components, could be applied to plug wrap 23 to enhance the subjective impact of the filtered smoke. A similar result might be achieved by forming plug wrap 23 from a tobacco-containing material, such as reconstituted tobacco sheet. Plug wrap 23 is preferably porous, to allow smoke and air to freely move radially between peripheral layer 20 and core 21. At the same time, the presence of plug wrap 23 helps prevent channelling of smoke along the interface between peripheral layer 20 and core 21. The most preferred embodiment of filter 12 has a circumference of about 24.45 mm and an average weight of about 258 mg. The cross-sectional area of core 21 preferably makes up about 60% of the total cross-sectional area of filter 12. Filter 12 preferably has an RTD of between about 110 mm W.G. and about 230 mm W.G., with the RTD of central core 21 being between about 300 mm W.G. and about 500 mm W.G.. More preferably, filter 12 has an RTD of about 146 mm W.G., with the RTD of central core 21 being about 400 mm W.G. In the particularly preferred embodiment, the cellulose acetate tow of peripheral layer 20 is preferably an 8.0/30000 cellulose acetate tow having a denier per fiber of 8, a total denier of 30,000, and a "Y" cross-sectional shape. The web of core 21 is preferably a 100% cellulose semi-creped softwood pulp paper with 10% crosswise creping for added tensile strength and elongation properties. Such a paper is available from Tela Papierfabrik AG, of Balsthal, Switzerland. Cigarette 10 is preferably ventilated to between about 50% and about 75% ventilation, and more preferably about 67% ventilation, with appropriate ventilation holes 15 provided in tipping 14. If the surface of filter 12 is not air permeable, appropriate holes would also be provided in filter 12. The core 21 is loaded with carbon particles 24 which are preferably uniformly distributed throughout core 21. One way of distributing the particles is to drop them from a vibratory conveyor onto the corrugated web before it is gathered and wrapped to form core 21. Preferably, the particles, once distributed onto the web, are kept in place by a liquid tack solution, such as a dilute solution of hydroxypropylcellulose (e.g., 7.5% by weight in water), which may be than sold by Aqualon Co., of Hopewell, Virginia, under the trademark KLUCEL®. The amount of the solution that is added is preferably about 1% by weight of the dry web. The filter plug 12 has between about 5 mg and about 35 mg, preferably about 10 mg, of carbon particles. The carbon particles have a size distribution such that about 94% of the particles are between about 20 mesh and about 70 mesh. The carbon particles have a moisture content between about 15.5% and about 20.5%, preferably about 18%, of their dry weight, and a carbon particle activity between about 50% and about 60%, preferably about 55%, CCl 4 activity. Filters according to the invention can exhibit about 85% reduction of gas phase in the filtered smoke. A reduction of about 17% is attributable to the carbon particles, with the remainder of the reduction attributable to the filter independent of the carbon particles. Fig. 3 shows a cigarette 50 having a second preferred embodiment of a filter 51 according to the invention. Filter 51 is a so-called "dual" filter, made up of two abutting filter segments 52, 53. Filter segment 52, which is adjacent tobacco rod 11, is a concentric filter as discussed above, in which the core 54 is of a web material containing carbon particles and peripheral layer 55 is of a tow material. Filter segment 53, which is at the mouth end, is a conventional tow filter, such as a cellulose acetate filter, and is provided primarily for cosmetic purposes. Nevertheless, segment 53 has filtration and RTD characteristics, and segment 52 must be adjusted so that the overall filter 51 has the desired characteristics. In a preferred form of this embodiment, segment 52 is constructed like filter 12, but has a length of only 18-20 mm, while segment 53 is a 7-9 mm long plug of 8.0/40000 cellulose acetate for tow having a denier per fiber of 8.0, a total denier of 40,000, and a "Y" cross-sectional shape. Total filter RTD is between about 100 mm W.G. and about 180 mm W.G., preferably about 160 mm W.G. The RTD of segment 53 is between about 10 mm W.G. and about 45 mm W.G., preferably about 14 mm W.G. The RTD of segment 52 is between about 85 mm W.G. and about 175 mm W.G., preferably about 146 mm W.G. The RTD of the paper core 54 of segment 52 is between about 195 mm W.G. and about 450 mm W.G., preferably about 357 mm. W.G. Cigarette 50 made with this embodiment of filter 51 is ventilated to between 50% and about 75% ventilation, preferably about 67% ventilation, with appropriate ventilation holes 15 in tipping 14. Fig. 4 shows a cigarette 60 having a third embodiment of a filter 61 according to the invention. Filter 61 is a recessed filter, made up of filter segment 62 recessed into tipping 14 at 63. Filter segment 62, which is adjacent tobacco rod 11, is a concentric filter as discussed above, in which the core 64 is of a web material containing carbon particles and peripheral layer 65 is of a tow material. The filter parameters discussed herein are valid for 85 mm and 100 mm cigarettes. It is to be understood that filters according to the present invention can also be used with longer cigarettes. If a longer cigarette is provided, the filter parameters would have to be adjusted, in accordance with the knowledge of those skilled in the art. EXAMPLE A filter according to the preferred form of the embodiment of FIG. 3, but using as the concentric filter segment the fifth preferred embodiment of this invention including 10 mg of carbon, was prepared and mated to an "ultra-light" king-size tobacco rod to produce a cigarette having the following characteristics: Tobacco 490 mg Total RTD 102 mm W.G. Filter RTD 161 mm W.G. Ventilation 68% Tipping length 32 mm The cigarette was smoked in a smoking machine with the following results: TPM 1.64 mg Nicotine 0.12 mg Water 0.12 mg "Tar" 1.4 mg Puff Count 6.0 The filter of this invention will improve the taste of low delivery cigarettes. It is also possible that the filter of this invention may offer similar performance at higher deliveries. For example, a medium delivery cigarette may be perceived as a full-flavor cigarette. Thus it is seen that a high efficiency filter which produces low delivery while also delivering acceptable taste and other aesthetic impacts is provided.

Claims: A smoking filter (12) (51) (61) comprising; a first filter plug (52) (62) comprising: a central core (21) (54) (64) of a gathered corrugated web filter material, and a peripheral layer (20) (55) (65) of a fibrous tow filter material surrounding the central core; the central core having a resistance-to-draw of between 285 mm W.G. and 500 mm W.G. and the filter having a resistance-to-draw of between 115 mm W.G. and 225 mm W.G., to, in use, initially direct a greater fraction of smoke through the peripheral layer than through the central core; the first filter plug (52) (62) further comprising: carbon particles (24) distributed throughout the central core, having a size distribution such that 94% of the particles are between about 20 mesh and about 70 mesh, a moisture content between 15.5% and 20.5% by dry weight of the carbon particles, and CCl 4 activity between about 50% and about 60%; and means (15) for admitting ventilation air into the peripheral layer, whereby smoke initially directed into the peripheral layer flows back into the central core. A smoking filter (12) (51) (61) according to claim 1 wherein the fibrous tow is cellulose acetate tow. A smoking filter (12) (51) (61) according to claim 2 wherein the cellulose acetate tow has a denier per filament of 8 and a total denier of about 30,000. A smoking filter (12) (51) (61) according to claim 1, 2 or 3 wherein the web material is paper. A smoking filter (12) (51) (61) according to claim 4 wherein the paper is creped before being corrugated and gathered into the filter. A smoking filter (12) (51) (61) according to claim 1, 2 or 3 wherein the web material is a nonwoven web. A smoking filter (12) (51) (61) according to claim 6 wherein the nonwoven web is cellulose acetate sheet. A smoking filter (12) (51) (61) according to any preceding claim wherein the gathered corrugated web material is wrapped in a plug wrap (22). A smoking filter (12) (51) (61) according to claim 8 wherein the plug wrap (22) is porous. A smoking filter (12) (51) (61) according to claim 8 or 9 wherein the plug wrap (22) contains flavor components. A smoking filter (12) (51) (61) according to claim 10 wherein the plug wrap (22) comprises a tobacco-containing material. A smoking filter (12) (51) (61) according to claim 11 wherein the tobacco-containing material comprises reconstituted tobacco sheet. A smoking filter (12) (51) (61) according to claim 10 wherein the plug wrap (22) comprises plug wrap paper to which flavor components have been added. A smoking filter (12) (51) (61) according to claim 13 wherein the flavor components comprise soluble tobacco components. A smoking filter (12) (51) (61) according to any preceding claim having a filtration efficiency of about 61% measured as if unventilated. A smoking filter (12) (51) (61) according to any of claims 1 to 15 having a filtration efficiency of about 76%. A smoking filter (12) (51) (61) according to any preceding claim having a ventilation rate of about 67%. A smoking filter (12) (51) (61) according to any preceding claim wherein the core (21) (54) (64) has a cross-sectional area occupying about 60% of the total cross-sectional area of the filter. A smoking filter (12) (51) (61) according to any preceding claim having a resistance-to-draw of about 146 mm W.G., the central core (21) (54) (64) having a resistance-to-draw of about 400 mm W.G. A smoking filter (12) (51) (61) according to any of claims 1 to 18 having a resistance-to-draw of about 135 mm W.G., the central core (21) (54) (64) having a resistance-to-draw of about 370 mm W.G. A smoking filter (51) according to any preceding claim further comprising a second filter plug (53) of cellulose acetate tow adjacent the first filter plug (52). A smoking filter (51) according to claim 21 wherein the first filter plug (52) has a resistance-to-draw of between 85 mm W.G. and 175 mm W.G., the central core (54) having a resistance-to-draw of between 195 mm W.G. and 450 mm W.G>, and the second filter plug (53) has a resistance-to-draw of between 10 mm W.G. and 45 mm W.G., so that the filter has a resistance-to-draw of between 100 mm W.G. and 180 mm W.G. A smoking filter (51) according to claim 22 wherein the first filter plug (52) has a resistance-to-draw of about 146 mm W.G., the central core (54) having a resistance-to-draw of about 357 mm W.G., and the second filter plug (53) has a resistance-to-draw of about 14 mm W.G., so that the filter has a resistance-to-draw of about 160 mm W.G. A smoking filter (61) according to any of claims 1 to 20 further comprising tipping (14) wrapped therearound, the tipping extending beyond one end of the first filter plug (62) for, in use, attaching the filter to a tobacco rod and extending beyond the other end of the first filter plug (62) forming a mouth-end recess (63) in the filter. A smoking filter (12) (51) (61) according to any preceding claim wherein the core (21) (54) (64) and the peripheral layer (20) (55) (65) are concentric. A smoking filter (12) (51) (61) according to any preceding claim comprising between about 5 mg and about 35 mg of carbon particles (24). A smoking filter (12) (51) (61) according to claim 26 comprising about 10 mg of carbon particles (24). A smoking filter (12) (51) (61) according to any preceding claim wherein the carbon particles (24) have a moisture content of about 18% by the dry weight of said carbon particles. A smoking filter (12) (51) (61) according to any preceding claim wherein the carbon particles (24) have a CCl 4 activity of about 55%. A smoking filter (12) (51) (61) according to any preceding claim wherein the carbon particles (24) are substantially uniformly distributed throughout the central core (21) (54) (64). A smoking filter (12) (51) (61) according to any preceding claim wherein the carbon particles (24) are held in place by an adhesive. A smoking article (10(50) (60) comprising a wrapped tobacco rod (11) (13) and a filter (12) (51) (61) according to any preceding claim.

Inventors: ARTERBERY CYNTHIA W, CALLAHAM W TIMOTHY, KERITSIS GUS D, LESLIE DONALD E, NEWMAN KENNETH A, SLAGLE ROGER S, WHITE JR MORRIS F, ARTERBERY, CYNTHIA W., CALLAHAM, W. TIMOTHY, KERITSIS, GUS D., LESLIE, DONALD E., NEWMAN, KENNETH A., SLAGLE, ROGER S., WHITE, JR., MORRIS F.
Applicants: PHILIP MORRIS PROD, PHILIP MORRIS PRODUCTS INC.
Application year: 1994
Main classification: A24D3
IPC codes: B01D53, A24D3, D01F2